1. Field of the Invention
This invention relates to exhaust cleaning devices for multi-cylinder internal-combustion engines and more particularly to those of the catalytic type.
2. Prior Art
Previously known in the art of multi-cylinder internal-combustion engines are high-power engines of the type including independent carburetors connected to the respective intake ports of the engine cylinders and independent exhaust pipes connected to the respective exhaust ports thereof. Such multiple carburetor and exhaust-pipe construction is aimed at maximizing the engine output per unit weight but, since the cylinders are each fed with a fuel-air mixture independently through the associated carburetor, more or less variations in air-fuel ratio are unavoidable between the mixtures fed to the respective cylinders on account of the manufacturing and assembly errors of the carburetors and associated parts. Also, variations in pulsation of exhaust gas flow can hardly be avoided between the independent exhaust pipes connected to the respective engine cylinders.
With this type of internal-combustion engine, it has been proposed for cleaning the engine exhaust to arrange catalytic converters in the respective exhaust pipes while feeding secondary air into the latter at locations upstream of the respective catalytic converters through reed valve means. With this arrangement, however, the catalytic converters are fed with exhaust gases differing in composition and volume of unburnt ingredients such as carbon monoxide (CO) and hydrocarbons (HC) on account of the non-uniformity in composition and volume of the air-fuel mixtures being fed to the respective engine cylinders. In addition, the amounts of secondary air introduced into the respective exhaust pipes are substantially different from each other due to variations in operation of the reed valves and pulsation of exhaust gas flows from the respective cylinders. Under these circumstances, the catalytic converters are unable fully to exhibit their cleaning performance as they are fed with secondary air at different flow rates while being fed with exhaust gases differing in composition and volume of unburnt ingredients and the cleaning efficiency of the entire system is impaired.